Lubricants, such as those used in a variety of machinery, are susceptible to oxidative deterioration during storage, transportation, and usage, particularly when such lubricants are exposed to high temperatures and iron catalytic environments, which greatly promote their oxidation. This oxidation, if not controlled, contributes to the formation of corrosive acidic products, sludge, varnishes, resins, and other oil-insoluble products and may lead to a loss of designated physical and tribological properties of the lubricants. These oxidation products may lead to the formation of harmful deposits on critical engine parts, such as the pistons, piston liners, valves, and valve lifters. It is therefore a common practice to include deposit-control and antioxidant additives in lubricants to prevent, at least to some extent, oxidation, so as to extend the useful life of the lubricants.
Lubricant compositions containing various secondary diarylamines as antioxidants are widely known in the art. The use of 1,4-benzenediamines is also known, as exemplified in U.S. Pat. Nos. 2,718,501, 2,883,362, 3,211,793, 3,304,285, and 5,711,767, U.S. Publication Nos. 2006/0128574, 2006/0189824, and 2007/0006855, GB1296592, and GB0835826 and JP59020392, the entire contents and disclosures of which are incorporated herein by reference. 1,4-benzenediamines have more commonly been employed as motor fuel stabilizers and antiozonants and antioxidants for rubber. There have been few reported 1,3-benzenediamines described suitable for use as antioxidants.
U.S. Pat. No. 2,451,642 discloses metaphenylenediamine, N1,N3-dimethyl-meta-phenylenediamine, and lauryl-meta-phenylenediamine as useful antioxidants for lubricating oil compositions for use in environments where iron-catalyzed oxidation reaction can take place. N,N′-dimethyl-ortho-phenylenediamine, N,N′-dicyclohexyl-para-phenylenediamine, and various di- and tetra-n-alkyl-para-phenylenediamines are similarly disclosed.
U.S. Pat. No. 2,857,424 discloses the preparation of oxalic acid salts of fuel stabilizing N,N′-dialkyl-para-phenylenediamines as a way of rendering the additives less toxic. The preparation of the oxalate salt of N,N′-dicyclohexyl-para-phenylenediamine is disclosed. The preparation of the oxalate salts of other unspecified dicycloalkyl ortho-, meta-, and para-phenylenediamines is contemplated.
Oberster, A. E. et al., 45 CAN. J. CHEM. 195-201 (1967), prepared 39 novel phenylenediamines as part of a program to find antiozonants for rubber that are not sensitizers or dermatotoxic. In some compounds the N′-phenylenediamine nitrogen was variously fused into a pyrrolidine, piperidine, hexamethyleneimine (homopiperidine), morpholine, or 2,6-dimethylmorpholine ring. In each case the N-cyclohexyl compound was prepared.
U.S. Pat. No. 3,402,201 discloses N,N′-dicyclooctyl-p-phenylenediamine as a stabilizer for organic materials, particularly rubber, and exemplifies its use as a gasoline inhibitor. The similar use of N,N′-dicyclooctyl-o- and m-phenylenediamines is contemplated.
Makogon, A. N. et al., 12 KHEMICHESKAYA PROMYSHLENNOST, SERIYA: METODY ANALIZA I KONTROLYA KACHESTVA PRODUKTSII V KHIMICHESKOI PROMYSHLENNOSTI 18-21 (1980), describe the characterization of N,N′-dialkyl-para-phenylenediamines reaction products obtained by the catalytic alkylation of 4-aminodiphenylamine with C7-C9 alcohols.
U.S. Pat. No. 4,487,759 discloses the use of certain tertiary phenylene diamines of the structure:

In particular, N,N′,N′-trialkyl-N-phenyl-para-phenylenediamines (e.g., N,N′-didecyl-N′-octyl-N-phenyl-para-phenylenediamine) is used as light stabilizers for unsaturated insect pheromones that are contained in a micro-encapsulation delivery system.
U.S. Pat. Nos. 5,207,939 and 5,312,461 disclose certain Mannich base reaction products of mono- or dialkyl-phenylenediamines, an aldehyde or ketone, and a hindered phenol, which can be used in an antioxidant amount in lubricating oils, greases, and fuel compositions. Specifically the phenylenediamines compounds have the formula:

Japan Patent No. 59-020,392 discloses a lubricant composition comprising N,N′-di-sec-butyl-para-phenylenediamine for pressure forming of oil tanks. The lubricant composition also contains hindered phenolic antioxidant.
The foregoing disclosures are incorporated by reference.
While phenylenediamines are known to act effectively as antioxidants, these compounds have been found to be disadvantageous commercially, since the presence of such compounds, when used in amounts conventionally used to provide antioxidancy, displayed adverse effects on piston deposit and varnish control and also displayed aggressiveness toward fluoroelastomeric engine seal materials. These adverse effects are particularly apparent with phenylenediamine compounds having higher nitrogen contents (compounds having relatively small hydrocarbyl substituents). Recent lubricating oil specifications for passenger car diesel engine lubricating oil (PCDO) set by original equipment manufacturers (OEMs) have required reduced levels of lubricant phosphorus (e.g., less than 800 ppm). To date, lubricating oil specifications for heavy duty diesel (HDD) engines have not limited phosphorus content, although the next generation of lubricant specifications (e.g., API CJ-4) is expected to do so. Expected limits on phosphorus content (such as to 1200 ppm or less), and reductions in the allowable amounts of sulfated ash (SASH) and sulfur will limit the amount of zinc dialkyldithiophosphate (ZDDP), one of the most cost-effective antiwear/antioxidant compounds, that a lubricant formulator can use.